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Influence of different living hinges geometries to compliant straight line mechanism trajectory
No full textClassical straight-line mechanisms are one of the most interesting, both from a theoretical and practical point of view. In many cases, those mechanisms frequently produce a nearly straight trajectory rather than one perfectly straight. In compliant form, those mechanisms can produce even better results. Compliant mechanism joints' deformability allows engineers to make further modifications. These modifications may improve the mechanism's ability to follow a straight path even further. This paper will provide an analysis of different hinge sizes, thicknesses, shapes, and overall geometrical characteristics. Their influence on the straightness of the mechanism trajectory will be analyzed and quantified
One-to-one mapping as a key factor in understanding the cardinality of sets among engineering students.
No full textThe use of different task formats (related to the same concept) has proven to be a good strategy
for eliciting cognitive conflicts and opportunities for deeper analysis of responses. Through its application, we
attempted to explore how engineering students deal with tasks related to the concept of set cardinality. The
study involved 269 students from two universities: the University of Belgrade and the University of Novi Sad.
By analyzing students’ responses, we discovered the most common misconceptions in solving such tasks and
why understanding the concept of functions (one-to-one mappings) played a crucial role. The results of this
research indicate the need for a thorough treatment of the concept of functions in elementary and high school, as
understanding this concept serves as a crucial foundation for further acquisition of more complex mathematical
concepts
APPLICATION OF 2D AND 3D DIGITAL IMAGE CORRELATION IN TESTING PRESSURE EQUIPMENT AND RELATED MATERIALS
No full textDigital Image Correlation (DIC) method, including both 2D and 3D DIC, plays an important
role in testing and evaluating pressure equipment integrity, as well as materials used in pressure
equipment. The 2D DIC method, employing a single-camera setup, is particularly suited for
assessing surface deformation and strain distribution in simpler geometries and thin-walled
pressure components under various loading conditions. This technique efficiently identifies
localized strains, surface defects, and initial crack formation, crucial for maintaining the
structural integrity of pressure vessels, piping, and storage tanks. Due to its ease of
implementation, 2D DIC is often applied in laboratory tensile tests, pressure cycle tests, and
validation of finite element models for flat or nearly flat pressure equipment surfaces.
On the other hand, 3D DIC, utilizing a stereo, dual-camera arrangement, significantly expands
the measurement capabilities, allowing accurate assessment of complex, three-dimensional
deformation fields present in curved or intricate geometries typical of pressure equipment. The
method effectively captures out-of-plane displacements and complex strain distributions arising
under internal pressure conditions, thermal loading, and fatigue tests, that are common
operational scenarios for pressure equipment. The advanced spatial measurement capabilities of
3D DIC enable precise identification of critical regions prone to failure, including weld joints,
nozzles, and geometrical discontinuities. Consequently, 3D DIC provides critical insights into
material behavior and structural response, enhancing safety, performance, and reliability in
pressure equipment.
Integrating DIC methodologies with advanced data processing techniques, further improves the
predictive capabilities and accuracy of strain measurements. These advancements facilitate early
damage detection and real-time structural health monitoring, significantly reducing the risk of
unexpected equipment failures. Ultimately, the focused application of 2D and 3D DIC in pressure
equipment testing supports more efficient design optimization, maintenance scheduling, and
regulatory compliance, reinforcing its importance within the domain of structural integrity
assessment
ANALIZA ALTERNATIVNIH REŠENJA GREJANJA GRADA POŽAREVCA U SLUČAJU GAŠENJA BLOKOVA TERMOELEKTRANE ”KOSTOLAC A1 I A2”
No full textNa osnovu objavljenih ciljeva Energetske zajednice u pogledu povećanja udela obnovljivih izvora energije u finalnoj potrošnji energije, smanjenja emisija gasova sa efektom staklene baste i povećanja energetske efikasnosti, potrebno je definisati dalji obim i dinamiku rada domaćih postrojenja na fosilna goriva. Termoelektrana "Kostolac A" pored električne energije proizvodi i toplotnu energiju. Trenutno je jedini izvor toplote za daljinsko grejanje dva gradska naselja (Požarevac i Kostolac) i 25 seoskih naselja. Eventualnom odlukom o gašenju ova dva bloka, potrebno je sagledati alternativna rešenja za snabdevanje toplotnom energijom pomenutih naseljenih mesta. U ovom radu je dat prikaz sedam alternativnih rešenja grejanja u slučaju gašenja blokova A1 i A2 Termoelektrane "Kostolac". U cilju pronalaska najprihvatljivijeg varijatnog rešenja, komparativno su sagledani i predstavljeni prostorni, ekonomski, energetski i ekološki aspekti.Based on the published goals of the Energy Community in terms of increasing the share of renewable energy sources in final energy consumption, reducing greenhouse gas emissions and increasing energy efficiency, it is necessary to define the further scope and working dynamics of domestic fossil fuel plants. Thermal power plant "Kostolac A" produces simultaneously heat and electricity. Currently, it represents the only heat source for district heating of two urban areas (Pozarevac and Kostolac) and 25 rural areas. In case of decision to shut down these two units, it is necessary to consider alternative heat sources for the supply of thermal energy to the mentioned populated areas. This paper outlines seven variant heating solutions in the event of shutdown of the TEKO A1 and A2 units. Spatial, economic, energy and ecological indicators are considered in order to identify the most acceptable variant solution
Mass Minimization of Axially Functionally Graded Euler–Bernoulli Beams with Coupled Bending and Axial Vibrations
No full textThe paper considers shape optimization of Euler–Bernoulli beams with circular, square and rectangular cross-sections made of axially functionally graded materials at a prescribed fundamental frequency. Optimization is carried out by the beam mass minimization. Considerations involve the case of coupled bending and axial vibrations, where complex boundary conditions are the cause of coupling. Pontryagin’s maximum principle is used to solve shape optimization, where a limited diameter or a beam cross-sectional width is used for control. Diameter limit is considered so that the optimized shape of a beam is within the limits of the validity of Euler–Bernoulli theory, and its strength does not decrease for smaller cross-sectional dimensions. The resulting system of differential equations is a two-point boundary value problem, and the shooting method is applied to solve it. The property of self-coupled systems is utilized, where all adjoint variables, except for one variable, are expressed through state variables, which facilitates solving the appropriate differential equations. Theoretical considerations are illustrated by an example. Also, the savings of beam mass in percent are determined, using the cantilever beam with optimal variable cross-section against the cantilever beam of a constant cross-section, where both beams have the same prescribed fundamental frequency
Examination of the Causes for Premature Failure of Mating Surfaces in Smart Injector Actuators
No full textFuel injector actuators in diesel engines are vital and widely used parts, particularly in hydraulics and fuel injection systems. They largely influence the technical, economic, and environmental quality of an engine. Therefore, it is of utmost importance for actuators to be highly reliable during their service life. Actuator reliability is a distinct feature of their mating surface performance. Due to complex operational conditions, increased surface stress, friction, and environmental impact, mating surfaces are exposed to various types of surface damage, wear, erosion, cavitations, and fatigue. Depending on the quality of production and the conditions they are used in, these damages are often generated much earlier than predicted, which is reflected in the reduction of the actuators' expected life span and reliability. In addition to the above, generated damage triggers the occurrence of other problems with fuel injection systems in diesel engines, resulting in increased fuel consumption and incomplete combustion, together with increased exhaust gas emission. The research conducted here analyzes the working performance of fuel injector actuators in diesel engines in heavy duty vehicles. The research is focused on inspecting the causes that lead to premature damage of mating surfaces
USING CFD AS A REPLACEMENT FOR EXPENSIVE EXPERIMENTS IN EDUCATION
No full textIn this paper, the authors analyzed the use of computational fluid dynamics (CFD) in education. The teaching of fluid mechanics today is mostly based on the theoretical approach. Although, throughout history, it has been shown that the earliest knowledge of fluid mechanics was gained through practical experience and experiments. Apart from this advantage, laboratory exercises and experiments also have numerous disadvantages. Experiments require significant financial resources, equipment and device maintenance. Many complex and specific experiments are not easy to perform in laboratory conditions. This leads to repeating the same experiments over generations. Student safety is also an important factor. During certain experiments, an increase in pressure or temperature may occur, leading to the risk of explosion or fire. Here we consider the possibility of replacing laboratory exercises by using CFD software. Computational fluid dynamics is gaining more and more importance as an alternative to classical laboratory exercises. This technology enables reliable virtual simulation of various fluid phenomena. The application of CFD in education would allow students to experiment with different parameters and scenarios without exposure to hazards, with more accurate and deeper data analysis. The paper also compares CFD software. Software is generally classified into two groups: open source and commercial software. Two open source software are presented in detail: OpenFOAM and SimFlow. On the example of airfoil NACA 0012, in both software, the simulation results were analyzed
CASCADED ILC-MPC CONTROLLER FOR ROBOT MANIPULATORS
No full textTrajectory tracking is one of the key aspects of robot control system design. High-precision
trajectory under disturbances, unmodeled dynamics, and parametric uncertainties of robotic
systems is a highly challenging task for multiple DoFs. Many different control approaches,
from simple PID controllers to advanced controllers such as Sliding Mode Control, Adaptive
Control, Robust Control, Fuzzy Control, and Model Predictive Control (MPC), are used within
trajectory tracking problems for robotic systems [1]. One of the control strategies suitable for
trajectory tracking problems for systems executing repetitive tasks is Iterative Learning Control
(ILC) [2]. The ILC is an intelligent, memory-based control method aimed at improving the
transient response performance of the system that operates repetitively over a fixed time
interval [3]. Several papers tackle improving the MPC with iterative learning controllers [4],
[5]. This research presents the integration of MPC and ILC using a simple structure consisting
of a cascaded ILC and MPC controller (Fig. 1.a) for position control of the robot manipulator.
The motivation for the cascaded structure is that the ILC controller does not interfere with the
MPC controller’s nonlinear optimization solver since the parallel structure of the ILC and MPC
would make MPC’s objective function more complex.
The proposed control system is verified via numerical simulation on a two-degree-offreedom
planar manipulator (Fig. 1.b). The constant disturbance (time and iteration-wise) is
considered in the simulation model. The reference trajectory in joint space is set to be a cubic
polynomial. The performance of the proposed control system is evaluated using Maximal
Absolute Error (MAE).
For each iteration, MAE is calculated and plotted as shown in Fig. 2.a, from which it can be
concluded that the ILC controller reduces the tracking error for both joints in approximately
four iterations. Fig. 2.b shows that the first joint tracks the reference trajectory almost perfectly
while the second joint has a larger tracking error, although still significantly reduced in
comparison to the sole MPC controller.The proposed Cascaded ILC-MPC control solution for robotic systems shows promising results. Further investigation should encompass the reduced dynamics model in the MPC and the fractional derivative in the ILC
Design and flow simulation of a morphing airfoil
No full textTo increase the efficiency of lifting surfaces, such as wings, tails, propeller or wind turbine
blades, the concept of morphing (changeable) geometry is gaining popularity and being more
and more investigated [1]. With the advances in materials, flexible structures, new production
techniques and improved simulations, it is possible to design optimal shapes for particular
operating conditions (e.g. low Reynolds numbers), that at the same time have the capability to
adapt to a wide range of different working conditions (that are present with small unmanned
air vehicles in urban environments). Here, one such airfoil contour is presented in Fig. 1(left),
and investigated in more detail. Geometric variations are achieved by vertically sliding three
key spinal points (at axial positions corresponding to 20%, 40% and 60% chord length) where
fixed-length ribs defining the outer (upper and lower) surfaces are perpendicularly connected.
Flow simulations by Reynolds-averaged Navier-Stokes (RANS) equations closed by transition
SST turbulence model are employed for the estimation of its aerodynamic performance,
example in Fig. 1(right). Very promising results are achieved that justify further research work
in this field
Machine Learning Within Industry 4.0: From Decision Trees to Visual Transformer Architecture
No full textMachine learning models have been revolutionizing the manufacturing
industry for a decade now. Many powerful models have been developed to solve
previously thought not solvable problems. In the era of rapid development of the
machine learning field, the selection of optimal models for the considered problem
within the Industry 4.0 setting is still a hard question. In the frist part of this work , we
provide an overview of the use cases of machine learning for Industry 4.0. Afterwards,
we provide details of the most commonly utilized machine learning models. Finally, the
experimental evaluation is performed to compare the analyzed models for two different
use cases, namely visual inspection and predictive maintenance. Two machine learning
models are compared for each task in order to highlight the main differences and
experimental results